1. Field of the Invention
The present invention relates to a distributed feedback semiconductor laser.
2. Related Background Art
Distributed feedback lasers have a Bragg grating that uses a cladding layer of InP semiconductor and a SCH layer for separated confinement heterostructure (SCH), and light from an active layer is diffracted by the index difference between the SCH layer and the cladding layer of InP semiconductor. After forming the SCH layer by crystal growth technique, the Bragg grating is formed by etching. When the SCH layer is made of AlGaInAs, it is known that the crystal quality is deteriorated because of aluminum oxidation and so on in the etching of the AlGaInAs layer. In the SCH layer of AlGaInAs, the Bragg grating is formed in the InGaAsP layer grown on the AlGaInAs layer in order to obviate the aluminum oxidation. In order to prevent the increase of electrons overflowed from the active layer to the p-type cladding layer, a carrier stop layer of AlInAs may be provided between the SCH layer and the Bragg grating formation layer.
Publication 1 (K. Nakahara, et al., 1.3-umInGaAlAs directly modulated MQW RWG DFB lasers operating over 10 Gb/s and 100 degrees Celsius, Central Research Laboratory Hitachi Ltd., OFC2004, ThD1)